diff --git a/pywwt/core.py b/pywwt/core.py
index 88a3e9eb..5c3c1ac2 100644
--- a/pywwt/core.py
+++ b/pywwt/core.py
@@ -21,6 +21,7 @@
 from .imagery import get_imagery_layers, ImageryLayers
 from .instruments import Instruments
 from .layers import LayerManager
+from .logger import logger
 from .solar_system import SolarSystem
 from .traits import Color, Bool, Float, Unicode, AstropyQuantity
 from .utils import ensure_utc
@@ -145,6 +146,7 @@ def __init__(self, hide_all_chrome=False):
         self._last_sent_view_mode = 'sky'
         self.layers = LayerManager(parent=self)
         self._annotation_set = set()
+        self._callbacks = {}
 
         if hide_all_chrome:
             self._send_msg(
@@ -320,6 +322,8 @@ def _on_app_message_received(self, payload):
         ptype = payload.get('type')
         # some events don't have type but do have: pevent = payload.get('event')
 
+        updated_fields = []
+
         if ptype == 'wwt_view_state':
             try:
                 self._raRad = float(payload['raRad'])
@@ -336,6 +340,18 @@ def _on_app_message_received(self, payload):
             if hipscat is not None:
                 self._available_hips_catalog_names = hipscat
 
+        elif ptype == 'wwt_selection_state':
+            most_recent = payload.get('mostRecentSource')
+            sources = payload.get('selectedSources')
+
+            if most_recent is not None:
+                self._most_recent_source = most_recent
+                updated_fields.append('most_recent_source')
+
+            if sources is not None:
+                self._selected_sources = sources
+                updated_fields.append('selected_sources')
+
         # Any relevant async future to resolve?
 
         tid = payload.get('threadId')
@@ -348,6 +364,39 @@ def _on_app_message_received(self, payload):
             else:
                 fut.set_result(payload)
 
+        # Any client-side callbacks to execute?
+
+        callback = self._callbacks.get(ptype)
+        if callback:
+            try:
+                callback(self, updated_fields)
+            except:  # noqa: E722
+                logger.exception('unhandled Python exception during a callback')
+
+    def _set_message_type_callback(self, ptype, callback):
+        """
+        Set a callback function that will be executed when the widget receives a message with the given type.
+
+        Parameters
+        ----------
+        ptype: str
+            The string that identifies the message type
+        callback: `BaseWWTWidget`
+            A callable object which takes two arguments: the WWT widget instance, and a list of updated properties.
+        """
+        self._callbacks[ptype] = callback
+
+    def set_selection_change_callback(self, callback):
+        """
+        Set a callback function that will be executed when the widget receives a selection change message.
+
+        Parameters
+        ----------
+        callback:
+            A callable object which takes two arguments: the WWT widget instance, and a list of updated properties.
+        """
+        self._set_message_type_callback('wwt_selection_state', callback)
+
     def _get_view_data(self, field):
         if not self._appAlive:
             raise ViewerNotAvailableError()
@@ -892,6 +941,30 @@ def available_hips_catalog_names(self):
         """
         return sorted(self._available_hips_catalog_names)
 
+    # Support for source and HiPS catalog selection
+
+    _most_recent_source = None
+
+    @property
+    def most_recent_source(self):
+        """
+        The most recent source selected in the viewer, represented as a dictionary.
+        The items of this dictionary match the entries of the Source object detailed
+        `here <https://docs.worldwidetelescope.org/webgl-reference/latest/apiref/research-app-messages/interfaces/selections.source.html>`_.
+        """
+        return self._most_recent_source
+
+    _selected_sources = []
+
+    @property
+    def selected_sources(self):
+        """
+        A list of the selected sources, with each source represented as a dictionary.
+        The items of these dictionaries match the entries of the Source object detailed
+        `here <https://docs.worldwidetelescope.org/webgl-reference/latest/apiref/research-app-messages/interfaces/selections.source.html>`_.
+        """
+        return self._selected_sources
+
     # Annotations
 
     def clear_annotations(self):
diff --git a/pywwt/tests/data/refimg_qt_full_step2/e.png b/pywwt/tests/data/refimg_qt_full_step2/e.png
new file mode 100644
index 00000000..b8783dec
Binary files /dev/null and b/pywwt/tests/data/refimg_qt_full_step2/e.png differ
diff --git a/pywwt/tests/data/refimg_qt_full_step3/e.png b/pywwt/tests/data/refimg_qt_full_step3/e.png
new file mode 100644
index 00000000..977f6659
Binary files /dev/null and b/pywwt/tests/data/refimg_qt_full_step3/e.png differ
diff --git a/pywwt/tests/data/refimg_qt_full_step4/e.png b/pywwt/tests/data/refimg_qt_full_step4/e.png
new file mode 100644
index 00000000..eaf4fa3f
Binary files /dev/null and b/pywwt/tests/data/refimg_qt_full_step4/e.png differ
diff --git a/pywwt/tests/data/refimg_qt_full_step5/e.png b/pywwt/tests/data/refimg_qt_full_step5/e.png
new file mode 100644
index 00000000..d4e8cf6b
Binary files /dev/null and b/pywwt/tests/data/refimg_qt_full_step5/e.png differ